Halogen light bulbs such as the MR-16 bulb are designed to produce a collimated beam of light via a parabolic reflector. Because halogen bulbs generate considerable energy in the infrared portion of the spectrum, it is often desirable to remove that invisible, heat-producing radiation from the primary illuminating beam. Typically this filtering of the infrared light is accomplished via the use of a dichroic parabolic reflector that is designed to transmit much of the infrared light while ideally reflecting and collimating the visible light, thus removing the infrared light from the primary illuminating beam. However, dichroic reflectors are typically imperfect reflectors and thus allow the transmission of a measurable amount of the visible light. In exemplary bulbs, this amount of “lost” transmitted light can amount to 20% of the total light produced by the bulb. Furthermore, this lost light is often not white light, as it acquires a color as a result of the interference properties of the dichroic reflector in the visible range of wavelengths. Red and green color hues are common in this secondary light, which is also referred to herein as “decorative light.” The light is also often patterned as a result of the shape of the dichroic reflector, as the glass on which the reflector is formed often has a faceted or otherwise textured surface.
The manufacturers of light fixtures have utilized decorative light in creative ways. For example, in pendant lights, the glass shade surrounding an MR-16 lamp is often illuminated by the light passing through the dichroic reflector, rendering visible the shade's decorative elements. If no such light were present, the entire fixture would be dark, and the attractive features of the fixture would be lost. This lack of decorative light plagues conventional light bulbs based on light-emitting diodes (LEDs). Although LED bulbs are much more energy efficient than halogen bulbs, their use is avoided in many applications because they do not produce decorative illumination.
One challenge in the production of decorative light arises because of the need to conform to the volume envelope of the standard bulb that the LED bulb is replacing. This defining shape restricts the volume envelope into which the numerous components of an LED bulb must fit; these components may include drive electronics, one or more LEDs, a heat sink, and a standard bulb base, leaving little if any room for components designed to provide decorative illumination. Additional constraints include the desire to reproduce the light pattern emitted by the standard halogen or incandescent bulb, as well as the desire to decrease costs.